<?xml version="1.0"?>
<html xmlns:svg="http://www.w3.org/2000/svg">
<!-- 声明HTML作为默认的命名空间，以"svg:"前缀的为SVG的命名空间-->
<body>
  <div>
  This is a red square:
  <svg width="100" height="100">
    <rect x="0" y="0" width="100" height="100" fill="red"/>
  </svg>
</div>

<div>
  This is a blue circle:
  <svg width="100" height="100">
    <circle cx="50" cy="50" r="50" fill="blue"/>
  </svg>
</div>
  
<div>
  This is a red round rectangle:
<svg width="400" height="180">
  <rect x="50" y="20" rx="20" ry="20" width="150" height="150" style="fill:red;stroke:black;stroke-width:5;opacity:0.5" />
  Sorry, your browser does not support inline SVG.
</svg>
</div>
</body>
</html>
